188 INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



Group B {Middle Chazy). 



FeDt. 



1. Impure nodular limestone, contaming Madur^a magna Lesueur 25 



2. Gray massive pure limestone, abounding in crinoidal fragments 20 



3. Bluish-black thick-bedded limestone, usually weathering so as to show pure nodular masses 



enveloped in a somewhat impure lighter-colored matrix; everywhere characterized by 

 Maclurea magna. Near the middle of this mass, for a thickness of about 30 feet, the fossils 

 are silicified and of jet-black color. The more important, besides Maclurea, are species of 

 Strophomena, Orthis, and Orthoceras 210 



4. Dark compact fine-grained limestone, with obscure bedding, weathering to a light gray. 



This rock resists erosion and is the upper stratum at Bluff Point, sloping upward from the 

 lake at an angle of 5° to a height of 170 feet. In one exposure the basal portion is densely 

 oolitic. Fossils are infrequent, but at a single locality there were collected Orthis perveta 

 Con., Orthis platys Bill., Leptxna fasdata Hall, Asaphus canalis Con., Cheirurus polydorus 

 Bill., Harpes sp. und., Illsenus incertus Bill., Lichas minganensis Bill., Sphxrexochus 

 parvus Bill., and several undescribed species 20 



5. Bluish-black limestone like No. 3, but less pure, containing Madurea magna Lesueur, Orthis 



perveta Con., Strophomena incrassata Hall, Orthis borealis Bill. (?), Orthis disparilis Con., 



or 0. porcia Bill 75 



Total thickness of B 350 



Group C ( Upper Chazy) . 



1. Dove-colored compact limestone, in massive beds, containing a large species of Orthoceras, 



Placoparia {Calymene) multicosta Hall, Solenopora compacta, and a large Bucania 60 



2. Dark impure limestone, in thin beds, abounding in Rhynchonella plena; at the base a bed 



4 dr 5 feet thick is filled with various forms of Monticulipora or Stenopora 125 



3. Tough arenaceous magnesian limestone, passing into fine-grained sandstone 17 



Total thickness of C : 202 



Aggregate thickness of the Chazy on Valcour Island 890 



Raymond ^®°' *^^ gives a classification of the faunal divisions of the Chazy 

 (Herbertella exfoliata division, Maclurites magna division, and Camarotaechia plena 

 division) and distinguishes a number of faunal zones. He also discusses the distri- 

 bution and correlation of the formation so far as it has been identified in Canada 

 and the United States. 



The belt east of the Hudson has been mapped by Dale ^' ^* from Lake Cham- 

 plain south to the Kinderhook (latitude 42° 30') . The rocks are chiefly slate, range 

 in age from Lower Cambrian to Lorraine, and are but sparsely fossiliferous. The 

 areal distribution of distinct formations is not worked out and the divisions mapped 

 by Dale are broad and indefinite. 



The post-Beekmantown Ordovician is included under the term "Hudson" and 

 the stratigraphy is summed up as follows : ^^^ 



